The present invention relates generally to the field of transducer communication through walls, and in particular to simultaneous use of multiple pairs of transducers to communicate via multiple channels through a single wall, and to suppressing interfering cross-talk between non-paired transducers.
A transducer is a device that converts one form of energy to another. Transducers may be used, among other functions, to transmit and receive data and power across a solid barrier without requiring any holes in the barrier. Conceptually, this can be done by a first transducer on one side of a barrier turning electrical energy into mechanical energy, the mechanical energy traveling across the barrier, and being received by a second transducer on the other side of the wall which converts some portion of the mechanical energy back into electrical energy. This ability is particularly useful for transmitting energy and data through barriers like ship and submarine hulls, pressure vessel tanks, and other walls separating extreme environments where it is undesirable to create physical openings for wires.
Ideally, transducer devices should be attached directly to the communications barrier, though many arrangements are possible. It is generally desirable to have a smooth, uninterrupted, uniform barrier between coupled transducers.
When two or more closely spaced pairs of axially aligned acoustic-electric (i.e. piezoelectric) transducers are mounted on opposite sides of a barrier or wall, undesired crosstalk occurs. This crosstalk occurs when signals sent by a first transducer on one side of the wall are received by transducers other than its intended mate on the other side of the wall. This crosstalk degrades signal processing between the aligned pairs.
Published patent application US2010/0027379, published Feb. 4, 2010 and incorporated herein by reference, discloses an ULTRASONIC THROUGH-WALL COMMUNICATION (UTWC) SYSTEM for communicating digital information through a barrier in the form of a thick metal wall, using ultrasonic techniques so that no through-holes are needed in the barrier. Using this system, signals can be transmitted through the barrier. For example, sensor signals that monitor conditions on one side of the barrier can be transmitted to the other side of the barrier. The barrier may be the wall of a pressure vessel and the conditions to be monitored may be those of a hostile, high temperature and high pressure, gaseous or liquid environment in the pressure vessel.
U.S. Pat. No. 7,902,943 to Sherrit et al. discloses a WIRELESS ACOUSTIC-ELECTRIC FEED-THROUGH FOR POWER AND SIGNAL TRANSMISSION including a first piezoelectric transducer to generate acoustic energy in response to electrical energy from a source, and a second piezoelectric transducer to convert the received acoustic energy to electrical energy to be used by a load.
U.S. Pat. No. 7,894,306 to Martin et al. for an APPARATUS AND METHOD FOR DATA TRANSFER THROUGH A SUBSTRATE discloses transferring data through a submarine hull or other solid boundary using high frequency acoustic signals to avoid penetration of the hull or boundary.
U.S. Pat. No. 5,982,297 to Welle discloses an ultrasonic data communication system including first and second transducers coupled together through a coupling medium for communicating input and output undulating pressure waves between the transducers for the transfer of input and output data between an external controller and an embedded sensory and actuating unit. An internal processor powers the second embedded transducer to generate ultrasonic waves into the medium that are modulated to send the data from the embedded sensor so that considerable energy is needed for the embedded circuits.
Also see U.S. Pat. Nos. 6,625,084; 6,639,872; 7,514,844; 7,525,398 and 7,586,392 for other approaches to the transmission of data or power through a barrier using ultrasound.
A more comprehensive approach to wireless data and power transmission through a barrier is taught by R. Primerano in “High Bit-rate Digital Communication through Metal Channels,” PhD dissertation, Drexel University, July 2010, hereafter referred to as Primerano. Without conceding that Primerano is prior art to the invention disclosed in the present application, Primerano is interesting because it teaches Orthogonal Frequency-Division Multiplexing or OFDM modulation with a cyclic prefix to send data at a high rate through a metal wall using ultrasound. The use of OFDM compensates for signal loss due to echos caused by boundaries or due to other incongruities across the channel.
Using transducers to send vibrational signals through a wall presents special challenges. Unlike more traditional arrangements, completely separate channels, such as separate wires, cannot easily be provided to segregate communication between different components and in different directions between the same components, or even to segregate power transmission from signal transmission. In many cases all communications—in both directions—must be passed through the same solid wall between multiple pairs of transducers.
Despite the technical obstacles, it is sometimes desirable to use multiple pairs of transducers to create multiple communication channels in the same section of a barrier wall. In theory more pairs of transducers means that data can be transferred at a faster rate, though in practice neighboring transducers often interfere with each other. Reducing or filtering out this interfering noise is thus highly desirable.
Multicarrier modulation schemes, such as orthogonal frequency division multiplexing (OFDM), and multichannel techniques, such as multiple-input multiple-output (MIMO), enable high rate wireless communication for wireless air channels. OFDM is a powerful alternative to single carrier schemes for achieving high data rates on frequency selective channels without requiring highly complex equalization. See, for example, J. Mietzner, R. Schober, L. Lampe, W. Gerstacker, and P. Hoeher, “Multiple-antenna techniques for wireless communications—a comprehensive literature survey,” Communications Surveys Tutorials, IEEE, April 2009; Y. Fu, C. Tellambura, and W. A. Krzymien, “Transmitter precoding for ICI reduction in closed-loop MIMO OFDM systems,” Vehicular Technology, IEEE Transactions on, January 2007. MIMO techniques have come to the forefront in recent years, employing multiple transmitters and/or receivers to increase reliability or to increase throughput capabilities. In combination, MIMO and OFDM have proven extremely effective at achieving high data rates with high reliability on frequency selective dynamic air channels.
There are many applications in which it would be beneficial to communicate wirelessly through enclosed metallic vessels at high data rates. Wired solutions involve drilling holes for wires which can be costly and reduce structural integrity. While electromagnetic transmission techniques employing multicarrier and multichannel approaches have proven extremely effective in the case of wireless air channels, such techniques are historically ineffective for wireless communication through metallic barriers due to Faraday shielding. Several alternative solutions have been presented which utilize the favorable propagation characteristics of ultrasound in metals. Most of these solutions have employed a single acoustic channel consisting of a pair of ultrasonic transducers mounted on opposite sides of a metallic barrier. Several single carrier, single channel systems have been presented whose data rates have been limited by inter-symbol interference (ISI) caused by the frequency selective channel. See, for example, G. J. Saulnier, H. A. Scarton, A. J. Gavens, D. A. Shoudy, T. L. Murphy, M. Wetzel, S. Bard, S. Roa-Prada, and P. Das, “Through-wall communication of low-rate digital data using ultrasound,” in Ultrasonics Symposium, 2006. IEEE, October 2006; D. A. Shoudy, G. J. Saulnier, H. A. Scarton, P. K. Das, S. Roa-Prada, J. D. Ashdown, and A. J. Gavens, “An ultrasonic throughwall communication system with power harvesting,” in Ultrasonics Symposium, 2007. IEEE, October 2007; R. Primerano, M. Kam, and K. Dandekar, “High bit rate ultrasonic communication through metal channels,” in 43rd Annual Conference on Information Sciences and Systems, CISS, March 2009.
In the Applicants' previous work they have used multicarrier modulation on a single channel utilizing 4096 OFDM subcarriers and achieved 12.4 Mbps communication through a 63.5 mm (2.5 in) thick steel barrier with an estimated maximum single channel capacity of 48 Mbps. Without admitting or denying that any particular reference constitutes prior art, see T. J. Lawry, G. J. Saulnier, J. D. Ashdown, K. R. Wilt, H. A. Scarton, S. Pascarelle, and J. D. Pinezich, “Penetration-free system for transmission of data and power through solid metal barriers,” in MILITARY COMMUNICATIONS CONFERENCE, 2011—MILCOM 2011, November 2011; T. Lawry, “A high performance system for wireless transmission of power and data through solid metal enclosures,” Ph.D. dissertation, Rensselaer Polytechnic Institute, July 2011.
See also S. H. Ting, K. Sakaguchi, and K. Araki, “A robust and low complexity adaptive algorithm for MIMO eigenmode transmission system with experimental validation,” Wireless Communications, IEEE Transactions on, July 2006.
U.S. Pat. No. 6,826,965 to Liu uses acoustics and crosstalk suppression in a measurement system that does not relate to communications. U.S. Pat. No. 5,539,832 to Weinstein et al. describes a technique for separating signals. U.S. Pat. No. 6,951,133 to Passarelli, Jr. Relates to non-destructive testing that seeks to find flaws in metallic structures. It describes electromagnetic transducers while this invention preferably uses piezoelectric transducers. U.S. Pat. No. 7,167,606 to Gunn, III et al. describes an optical waveguide. US 2002/0122464 to Dodge uses Walsh function amplitude modulation.